1. Field of the Invention
The present invention relates to an image reader employed in an MFD (Multi Function Device), etc., and particularly relates to a structure of a contact image sensor which is incorporated in an image reader.
2. Description of the Related Art
Conventionally, a CCD sensor or a contact image sensor (CIS) is used as a sensor of an image reader. A CCD sensor is constructed of a light source, a mirror, a lens, a CCD and the like. Image reading is performed by the light source illuminating light onto a document (original) and the CCD receiving the reflected light, and has a feature that a focal length is secured by using a plurality of mirrors to make the reflected light be converged to the lens.
For example, a supporting structure of a scanner unit which uses a CCD is disclosed in Japanese Patent Application Laid-open No. 2002-229133.
Meanwhile, with a CIS, light emitted from a light source irradiates a document, and image reading is performed by the reflected light being received by a light receiving element. Normally, a plurality of light receiving elements are positioned in array form with respect to a reading area (reading region). To irradiate incident light onto or receive reflected light from the reading area reliably, the CIS is positioned in close contact with a glass plate on which a document is placed. A member and the like which urges the CIS into close contact with the glass plate is thus required.
For example, in an image sensor disclosed in Japanese Patent Application Laid-open No. 10-285342, in a process of reading a document, the document is fed while being put in close contact with a cover glass by a roller and the like.
FIG. 11 is an exploded perspective view of a fixing structure for a close-contact image sensor in an image reader described in Japanese Patent Application Laid-open No. 2005-3778. This close-contact image sensor 1 has a sensor on an upper surface thereof, and has positioning portions 7a and 7b and a fixing projection 5 on a side of the lower surface of the close-contact image sensor 1. The positioning portion 7a is disposed on one side surface (at the front left side in FIG. 11) in a short direction of the close-contact image sensor 1, substantially at the center in a longitudinal direction of the close-contact image sensor 1, and the positioning portion 7a is constructed of ribs 8a and 8b extending vertically downward from a lower end of the close-contact image sensor 1, and a groove 9a formed or defined by the ribs 8a and 8b. Here, the ribs 8a and 8b are formed at a spacing distance or interval which is substantially equal to the diameter of a shaft 4. The positioning portion 7b is disposed on the other side surface (at the inner right side in FIG. 11) facing the positioning portion 7a and is constructed of the ribs 8c and 8d extending vertically downward from the lower end of the close-contact image sensor 1, and a groove 9b defined by the ribs 8c and 8d. Here, the ribs 8c and 8d are also formed at a spacing distance which is substantially equal to the diameter of the shaft 4. The fixing projection 5, having a cylindrical form of predetermined diameter and predetermined length, is disposed so as to extend vertically downward from the lower end of the close-contact image sensor 1 at the substantially central position of the close-contact image sensor 1. The positioning portions 7a, 7b and the fixing projection 5 are formed integral to the close-contact image sensor.
A bracket 3 is positioned below the close-contact image sensor 1 and has a plurality of through holes 12a, 12b, and 15 at the substantially central portion of the bracket 3. In the bracket 3, the through hole 15 is formed at a position opposing to the fixing projection 5 of the close-contact image sensor 1, and the through holes 12a and 12b are formed at positions opposing projections 22a and 22b, respectively, of a bearing 2 which will be described later. Also, the bracket 3 has spring fixing portions on upper surface side, in the vicinity of both ends, respectively, in the longitudinal direction of the close-contact image sensor 1, and has springs 11 fixed onto the spring fixing portions, respectively.
The bearing 2 has, at its lower end, a groove 21 which engages with the shaft 4, and has, on its upper end surface, projections 22a and 22b and a recess 25. The groove 21 is formed in a shape which substantially matches the outer diameter shape of the shaft 4, and the bearing 2 is attached or mounted to be movable along the axial direction of the shaft 4. Also, a belt fixing section 23, for connection to a driving belt 6, is provided on a side surface (front right surface in FIG. 11) of the bearing 2.
The bracket 3 is fixed to the bearing 2 by positioning the bracket 3 on an upper surface of the bearing 2 and fitting the projections 22a and 22b of the bearing 2 into the through holes 12a and 12b, respectively, of the bracket 3. Furthermore, the close-contact image sensor 1 is fixed to the bearing 2 by positioning the close-contact image sensor 1 above the bracket 3 via the springs 11, and by inserting the fixing projection 5 of the close-contact image sensor 1 through the through hole 15 of the bracket 3 so as to fit the fixing projection 5 into the recess 25 of the bearing 2. At this time, the positioning portions 7a and 7b of the close-contact image sensor 1 approach the respective side surfaces, in the axial direction of the shaft 4, of the bearing 2 to sandwich the shaft 4 by the ribs 8a and 8b of the positioning portion 7a, and to sandwich the shaft 4 by the ribs 8c and 8d of the positioning portion 7b. 
For an image to be read finely from a document, the longitudinal direction (primary scanning direction) of the close-contact image sensor needs to be orthogonal to the axial direction (secondary scanning direction) of the shaft when the close-contact image sensor is sliding. However, in the fixing structure of the close-contact image sensor in image reader described in Japanese Patent Application Laid-open No. 2005-3778, the close-contact image sensor is held by the bracket and the bearing and is attached or mounted onto the shaft such that the close-contact image sensor and the grooves formed on the bearing are engaged with the shaft. Accordingly, the precision of orthogonality of the primary scanning direction and the secondary scanning direction is thus determined by the precision of attachment for the shaft and the bearing, the precision of attachment for the bearing and the bracket, and the precision of attachment for the bracket and the close-contact image sensor. That is, for the primary scanning direction and the secondary scanning direction to be accurately orthogonal, high precision of attachment for the shaft and the bearing, high precision of attachment for the bearing and the bracket, and high precision of attachment for the bracket and the close-contact image sensor are required.
However, the operation or work for accurately making the primary scanning direction and secondary scanning direction orthogonal by mounting or attaching the bearing onto the shaft with high precision, by mounting or attaching the bracket onto the bearing with high precision, and by mounting or attaching the close-contact image sensor onto the bracket with high precision is not easily performed because errors of the three attaching or mounting operations accumulate. In addition, since the shaft, the bracket, and the bearing are required, the mechanism is complicated and the number of parts is great. This consequently leads to increased parts cost and assembly cost of the image reader, thereby increasing the manufacturing cost of the image reader.
Japanese Published Application Laid-open No. 09-261424 discloses an image reader constructed of a contact glass, a lead shaft, a driving wire, a slide bearing having a wire clamp, a grounded roller, and a leaf spring. The close-contact image sensor is pressed against the contact glass by the grounded roller and the leaf spring, and reads an image of a document placed on the contact glass as the slide bearing is sliding while being in contact with the lead shaft upon receiving a driving force from the driving wire engaged with the wire clamp.
In the image reader described in Japanese Patent Application Laid-open No. 09-261424, it is clearly disclosed that the housing of the close-contact image sensor is formed of aluminum. However, it is not clearly disclosed that the slide bearing is formed integral to the housing of the close-contact image sensor.